In the drilling of a bore into the earth with a rotary tool, it has been the almost universal practice up until recent years to circulate a liquid, such as water, oil, a water-in-oil emulsion, or an oil-in-water emulsion, usually with mud soilds suspended therein, to and from the drilling zone during the drilling operation. One of the functions in circulating these drilling fluids, usually in the form of a drilling mud, is to remove drilled solids from the bit and lift cuttings from the bore. As can be readily understood the drilling liquid must be circulated under high pressure to assure entrainment of cuttings and expulsion of mud from the bore hole.
In recent years, some wells have been successfully drilled at a reduced pressure by a different technique in which a compressed gas, such as air, is pumped into the well at the drilling site. This compressed gas flows rapidly up the well bore around the drill collar carrying with it the drilled solids and thus removing them from the drill hole. While in some instances, the drilling operation is essentially a dry process, in many formations, water high in electrolyte concentration, enters the bore hole from adjacent water-containing strata. Such water invasion most often occurs while drilling in or through a water bearing subterranean zone, but may also be encountered in any area in the vicinity of trapped underground water.
Some of the advantages of the gas drilling method over the more conventional mud drilling method include increased penetration rate, longer bit life, accurate location of water-bearing zones and measurement of flow, precise location of oil and gas bearing zones, especially those of low formation pressure, flow and pressure testing of productive zones without resort to drill stem tests, a lessening of possible contamination of prospective or known producing zones, and greater flexibility in physical-chemical alteration of the drilling fluid to meet particular down hole conditions. However, one difficulty in mist or dry gas drilling where water seeps into the bore and accumulates in the drilling zone, is that the drilled solids tend to agglomerate as the drill rotates. These agglomerated masses become too heavy to be lifted out by the gas so that antiballing agents, and foaming agents must be introduced into the bore to prevent this condition.
In recent years, the technology of air and mud drilling has been combined in an attempt to provide drilling foams which have greater lifting strength than air but which do not have the pressure limitations of drilling muds.
The rheological properties of aqueous foams are of great importance for a number of applications in petroleum production. These properties include high flow rates in tubes or pipes and in porous media such as oil-bearing sandstones. Aqueous foam has advantages in oil fields that contain viscous oil in low pressure reservoirs. In these operations, the foam raises to the surface not only sand pulverized by the bit but also pebbles and rocks of considerable size.
The requirements for utilization of an aqueous foam in subterranean formations include high stability with waters containing appreciable quantities of soluble salts, such as sodium chloride, calcium salts and/or magnesium salts and capability for handling a variety of foam breaking elements such as crude oil and solids. Further the foam must not degrade under extremes of physical environments.
Numerous foam compositions have been proposed and used, however most have proven unsatisfactory in one respect or another. Among the various classes of foaming compositions, are nonionics; however, these are affected by salts and high temperatures encountered in drilling. Although many anionic surfactants provide acceptable foams in soft waters, they form foam breaking precipitates in the presence of brine and/or hard water. Cationics are useless foamers because of their intolerance to high salinity. Although, amphoterics are medium foamers, they lack stability over periods required for removal of debris, usually above 3 minutes based on the pressure under which the foamer is introduced and the depth of the bore hole.
Accordingly, it is an object of this invention to overcome the deficiencies of air drilling and aqueous foam drilling fluids discussed above.
It is another object of this invention to provide an economical and commercially acceptable composition as a foaming agent in air or geothermal drilling operations.
Still another object of this invention is to provide a surfactant composition having excellent foaming power and high tolerance for aqueous solutions containing electrolytes and/or diesel oil.
Still another object is to provide a strong stable foam for use in wallboard manufacture, gypsum products or other uses which require a rigid foam.